# Using stage interface

 Register Blogs Members List Search Today's Posts Mark Forums Read

 October 20, 2010, 10:44 Using stage interface #1 Member   Join Date: Apr 2010 Posts: 33 Rep Power: 9 Sponsored Links Dear all, My question is regarding the use of a stage interface. I am modelling a fan blowing air through a radiator. Is it valid to model one fan passage out of seven and the entire radiator and to use a stage interface between the two? The radiator is square. In other words do I need to model the full fan for this case? I am considering using the downstream velocity constraint "constant total pressure" so that the downstream velcoity can be adjusted due to the impact of the radiator. Thanks, ijk

 October 21, 2010, 07:50 #2 Senior Member     Attesz Join Date: Mar 2009 Location: Munich Posts: 364 Rep Power: 10 With the stage option the fluxes will be averaged at the interfaces. The problem in your case is the high pitch ratio. You will get an 51deg periodic domain in a rotating frame of reference with the periodic side 1 and the radiator's stage will have 360 deg, so the pitch ratio will be about 7 which is high, and you can get very inaccureate results easily. I think, you should use the radiator as a periodic model, or if you can't do so, use the entire model. On the boundaries, mass flow or pressure values are better, except you have the velocity profile measured. If you can, post some picture about the geometry.

 October 26, 2010, 11:11 #3 Member   Join Date: Apr 2010 Posts: 33 Rep Power: 9 Thank you for your response. I cannot simulate one quarter of the radiator due to its heat transfer. I do not understand why the computational accuracy would degrade with increasing pitch change if the values of flow variables apart from pressure are simply averaged and passed downstream. The manual says: "The computational accuracy degrades rapidly with increasing pitch change. It is recommended that sufficient blade components be analyzed on each side of the interface to minimize pitch change. Any pitch change will result in a non-physical transient interaction: the entire 360 degree components must be solved for truly “accurate” transient interactions if the pitch ratio is non-integer. Small pitch changes will introduce relatively smaller errors, large pitch changes will introduce larger errors. "

 October 26, 2010, 22:31 #4 Senior Member   Michael P. Owen Join Date: Mar 2009 Posts: 196 Rep Power: 10 ijk, You are correct; the solution will not be degraded because of the pitch change, because it is an integer ratio (7). Now the real question you should be asking is not "Can I use a stage with a 7:1 pitch change" but rather, is a stage interface appropriate at all? If the latter is true, then the pitch change is irrelevant as long as it's integer. You need to calculate r*omega and compare it to the through velocity of the fan. If it's much greater than the through speed, then the stage approximation starts to become appropriate.

 October 27, 2010, 07:11 #5 Member   Join Date: Apr 2010 Posts: 33 Rep Power: 9 Thanks Michael, Your response helped clarify things a lot. My average through speed is about a fifth of the tip speed. Good to see you keep yourself busy with CFD whilst on the bench. How's the hamstring? ijk

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Saturn CFX 45 February 8, 2016 05:42 pad CFX 3 April 28, 2010 09:08 Pankaj CFX 9 November 23, 2009 05:05 Vikram CFX 2 October 21, 2005 04:55 lego CFX 3 November 5, 2002 21:09